Research on human embryonic stem cells has numerous potential medical applications, but should it be pursued at the risk of imperiling our collective moral soul and social infrastructure?

Imagine yourself, 12 years from now, sitting in your doctor's office. The doctor has just informed you that you have a serious, debilitating disease. Treatment options are limited. Describing these options and following the canons of informed consent, your physician neutrally adds a caveat about one: the therapy is derived from human embryos. You must make a choice. What would you do?

A hypothetical scenario? Maybe not. Although floating in legal limbo and ensnared in an ethical quagmire, human embryonic stem (ES) cell research will most likely continue. Flourishing in the private sector, it may soon gain further momentum from an influx of federal money.

It has been a tumultuous 12 months since November 1998, when two research groups independently announced that they had achieved a major technical breakthrough: They had isolated human stem cells from embryonic tissues, cultivated the cells in laboratories for several months, and shown that these cells could develop into all three basic layers of cells in the human embryo. Because these cells, under the right conditions, can potentially "differentiate" (develop) into nearly every type of cell and tissue in the human body, they hold great promise for applications in medicine as well as for research into human development.

Hearing the news, the biological research community buzzed with excitement. Harold Varmus, director of the National Institutes of Health (NIH), was quoted as saying that human ES cell research "had the potential to revolutionize the practice of medicine and improve the quality and length of life." At the same time, ethical and moral critiques resounded. The central concern expressed was that the techniques by which the stem cells were derived involved the destruction of human embryos, depriving them of their potential to develop into full human beings. A related concern is whether this research would open one more door by which some might tinker with human life, possibly in some grand experiment in eugenics. Will the efforts at pursuing the holy grail of regenerative medicine open up a Pandora's box of undesirable moral and social consequences?

The quest

Interest in embryonic stem cells dates back to at least 1981, when they were first cultured successfully from mouse embryos. Since then, ES cells have been isolated from various other animals, including sheep, hamsters, pigs, cows, rabbits, mink, rhesus monkeys, and marmosets. But culturing human ES cells proved difficult: Once isolated, they refused to stay undifferentiated, seemingly driven to spontaneously differentiate and form primitive structures. The first publicly anowledged attempt to isolate and culture ES cells from human embryos in vitro was published in 1994. That attempt was unsuccessful.

Given these difficulties, biologists were especially impressed when, on November 6, 1998, James Thomson and his research team at the University of Wisconsin, Madison, reported in Science that they had successfully maintained human ES cells in laboratory culture for a number of months. The cells were derived from "spare," week-old embryos produced by in vitro fertilization at a fertility clinic, after obtaining consent from the gamete contributors. Thomson's group further showed that the ES cells could differentiate into a variety of tissue types--including the gut lining, muscle, cartilage, bone, and neural epithelium-- representing derivatives of all three basic layers of the mammalian embryo.

Four days later, the work of John Gearhart and his group at Johns Hopkins University was published in the Proceedings of the National Academy of Sciences, announcing that they had isolated and grown similar stem cells in culture. Their work differed from Thomson's in two significant ways. …

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